700. Search in a Binary Search T

二叉搜索树中查找元素

时间复杂度为：O(H)，H为树的高度，平均时间复杂度O(logN)，最坏时间复杂度O(N)

空间复杂度：递归O(H)，迭代O(1)

• Runtime: 96 ms, faster than 76.47%
• Memory Usage: 45 MB, less than 73.82%

• 递归

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @param {number} val
 * @return {TreeNode}
 */
var searchBST = function(root, val) {
    if (root === null) return null
    if (root.val === val) return root
    if (root.val < val) return searchBST(root.right, val)
    if (root.val > val) return searchBST(root.left, val)
    return null
};

• 迭代

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @param {number} val
 * @return {TreeNode}
 */
var searchBST = function(root, val) {
    while(root !== null && root.val !== val) {
        root = root.val > val ? root.left : root.right;
    }
    return root
};